The invention relates to an arrangement for working (finishing) internal conical surfaces of metal parts having a hollow space with a high slenderness ratio, which hollow space is a cylindrical surface terminating in an inner coaxial conical surface. For the working in accordance with the invention, there is employed an electrode which is connected to one pole of a source of burning electrical impulses and the electrode, which terminates in a conical burning part, is provided with a guiding part insulated from the electrode and inserted in a guiding means for the electrode formed by a cylindrical surface of the hollow space of the workpiece. The workpiece is connected to the second pole of the source of burning electrical impulses. The electrode is in engagement with means for rotating it and also with means for its quick and/or microadvance with respect to the workpiece.
The accurate working (finishing) of internal conical surfaces terminating a hollow space of a metal workpiece having a high slenderness ratio, for instance the grinding of seats of some fuel injection bodies of Diesel engines, presents substantial difficulties.
A number of methods for the working of internal conical surfaces of workpieces of this kind are known, but all of them are either so costly or not sufficiently precise. A method called abrasive technology is for instance known. In this method a small grinding disk rotating at a high speed on the order of 70,000 rpm is used. The active part of the grinding disk is conical and is in contact with the ground conical surface, performing in addition to the mentioned rotational motion a straight line reciprocal motion in the direction of a geometrical element of the ground conical surface.
This grinding method requires means for generating high speed revolutions, which presents substantial problems at the required accuracy of grinding. It requires high grade and accurate grinding disks and also entails certain risks from the point of view of the safety of the operator. It is rather demanding on the operator or operators--particularly from the point of view of adjustment and of maintenance, since the high speed spindles used have a short lifetime. Another substantial drawback exists in addition to these unfavorable conditions, namely that this method cannot be practically applied in the accurate grinding of internal conical surfaces having a slenderness ratio higher than 1:8. Under these conditions this described method fails since, due to the use of relatively long spindles, not only problems arise with their supporting and driving at high speed, but also unwelcomed deformations of the spindles take place and thus there result imperfections of the required geometry of the conical surface.
Another known method uses the electroerosive principle in which working of conical surfaces proceeds by means of a wire electrode, wherein the workpiece rotates and the electrode performs a reciprocal motion, again in the direction of an element of the conical surface. A drawback of this method is that it cannot operate reliably even with a slenderness ratio of 1:6 due to lack of space, particularly also because of the springing and permanent deformation of the electrode, because of difficulties of adjustment, and extraordinary demands on the operators. As a result, there are imperfections in the required geometry of the ground surface.
An arrangement for working internal conical surfaces of metal workpieces with a hollow space having a high slenderness ratio is known. In such arrangement, the hollow space is a coaxial cylindrical surface terminating in a conical surface, and the working is performed by an electrode connected to a source of burning electrical impulses, and the electrode, the shaft of which terminates in a conical burning surface, is provided with a guiding part insulated from the shaft and is inserted in a means for guiding the electrode. Such grinding means is formed by a cylindrical surface of the hollow space of the workpiece. The workpiece is clamped in a workpiece fixture, which is connected to one pole and the electrode shaft is connected to the other pole of a source of burning electrical impulses. On a vertically slidable bridge, which is in engagement with a device for quick advance of the spindle, there are provided a drive for the rotation of the electrode and a driving source for its microadvance. It has been found that this arrangement, although it represented a substantial improvement for working internal conical surfaces of metal workpieces of this kind, is relatively complicated so far as the provision of quick and microadvance of the spindle is concerned, and furthermore that it does not permit an instantaneous stoppage in those cases wherein no electrical connection of the electrode with the worked conical surface takes place due to the presence of electrically non-conductive dirt between the electrode and the worked surface. It has been also found that the rinsing system, i.e. the removal of burning products, requires improvement.